1. Field of the Invention
The present invention relates to a communication technique, in particular, to a communication method for performing retransmission control between a transmitting apparatus and a receiving apparatus, and the transmitting apparatus utilizing the method. Also, the present invention relates to a communication technique, in particular, a communication method for performing communications between a transmitting apparatus and a receiving apparatus, and the transmitting apparatus utilizing the method.
2. Description of the Related Art
In a mobile communication system comprised of a radio base station and a radio mobile station, the radio base station assigns a channel to the radio mobile station as a resource. Also, communications are performed between the radio base station and the radio mobile station using the assigned channel (See Reference (1) in Related Art List, for instance).
Related Art List
    (1) Japanese Patent Application Publication No. 2006-270941.
In wireless communication, it is generally desired that the limited frequency resources be used effectively. With a growing communication rate in particular, such a demand is ever increasing. One of technologies that meet this request is a technique called OFDMA (Orthogonal Frequency Division Multiple Access). This scheme can be combined with TDMA/TDD. OFDMA is a technique where a plurality of terminal apparatuses are frequency-multiplexed using OFDM. In such OFDMA, a sub-channel is formed by a plurality of subcarriers, and a multicarrier signal is formed by a plurality of sub-channels.
The combining of the OFDMA scheme and the TDMA scheme allows the multicarrier signal to be divided into a plurality of time slots on the temporal axis. As a result, a base station apparatus performs data communication with a terminal apparatus by allocating a sub-channel in at least one time slot to the terminal apparatus. In order to improve the accuracy in the data communication, retransmission control is performed. In the retransmission control, sequence numbers are assigned to identify erroneous data. Such sequence numbers are said to be more important than the data. For this reason, the degree of reliability for communications through which the sequence numbers are transmitted should be set higher than the degree of reliability for communications through which data are transmitted. In order to cope with this, it is effective to define a field for use in control signal separately from a field for use in data and have a sequence number contained in the field for use in control signal. In so doing, the modulation scheme or the coding rate of error correction for the field for use in control signal is set to a more robust modulation scheme or a value higher than the value of the coding rate of error correction for the field for use in data.
There are cases where a plurality of kinds of retransmission controls are defined and any one of them is selected by a terminal apparatus and a base station apparatus when performing communication. When the type of retransmission control differs from one another, the length of the sequence numbers required or other information also differs. Hereinafter, the sequence numbers, other information and the like required for the retransmission control are referred to as “control information”. Accordingly, if a plurality of kinds of retransmission controls are to be all dealt with, the size of control information will be large. At the same time, in view of transmission efficiency, a design is made so that the size of the field for use in control signal becomes smaller. Even in such a case, the control information is required for retransmission control. Also, it is preferable that any change in the control information be properly dealt with in order to flexibly respond to the change of parameters in the retransmission control.
Since there are a plurality of kinds of data communication contents, there are a plurality of kinds of data assigned to each sub-channel. Generally, when the type of data differs, the quality required also differs. For example, audio data used for telephone communication or image data used for video telephones require the real-timeliness. The real-timeliness is not required for information data used for the file transfer. Instead, the accuracy is required for the information data used for the file transfer. Further, the control signal used to control the above-described data communication is assigned to the sub-channel as data.
Under such circumstances, the inventor of the present invention had come to recognize the following problems to be resolved. When the size of a sub-channel is defined beforehand, there are cases where the size of data to be transmitted is smaller than the size of the sub-channel. In such a case, the transmission efficiency will be improved if still another data can be assigned to the sub-channel. However, as described above, there are a plurality of kinds of data, so that there exists a combination of data which should not be contained in a single channel.